1. Field of the Invention
This invention relates to a magnetic head apparatus comprising a reproducing element with an MR head (reproducing head) mounted thereon, and wherein a piezoelectric element is mounted on a support member supporting the MR head. This invention also relates to a method of manufacturing the magnetic head apparatus. In particular, this invention relates to a magnetic head apparatus that has been improved to avoid damage to the MR head, as well as to a manufacturing method thereof.
2. Description of the Related Art
FIG. 10 is a top plan view of a conventional hard disk apparatus. A magnetic disk 1 is rotated by a spindle motor 2.
A load beam 4 constituting a support member is connected to the distal end 3a of a rigid carriage 3, and at the distal end 4a of a load beam 4, a slider 5 is fitted through a flexure (not shown).
The load beam 4 comprises a leaf spring. The load beam 4 has a fixed base end 4b which is fixed on the carriage 3. The distal end 4a of the load beam 4 supports the slider 5.
The slider 5 includes a reproducing element for detecting, by magnetoresistive effect, the magnetic signals recorded on the magnetic disk 1, and a recording element for recording magnetic signals on the magnetic disk 1. The slider 5 floats above the magnetic disk 1 by the action of air streams created by the rotation of the magnetic disk 1 so as to record and reproduce the magnetic signals.
A voice coil motor 6 is fixed to the base end 3b of the carriage 3.
By the action of the voice coil motor 6, the carriage 3 and the load beam 4 are driven in the radial direction of the magnetic disk 1, thus implementing a seeking operation for moving the reproducing element and the recording element mounted on the slider 5 to any recording track, as well as implementing a tracking operation for keeping the reproducing element and the recording element on the central line of a particular recording track.
The higher recording density of the magnetic disk 1 makes it necessary to improve the precision of tracking operations. Hitherto, the seeking operation and tracking operation have been carried out only by driving the carriage 3 by means of the voice coil motor 6.
In order to improve the precision of the tracking operation, it is necessary to raise the servo band of the servo system including the voice coil motor 6. The servo band, however, is limited by the mechanical resonance frequency of the carriage 3 and that of the bearing (not illustrated) rotatably supporting the carriage 3. The mechanical resonance frequency of the carriage 3 depends on the size of the carriage 3, which in turn depends on the diameter of the magnetic disk 1 prescribed by the standard. For example, when the diameter of the magnetic disk 1 is 3.5 inches, the resonance frequency of the carriage 3 and the bearing is about 3.5 kHz.
When the resonance frequency of the carriage 3 and the bearing is about 3.5 kHz, the upper limit of the servo band is approximately 700 Hz in a servo system that performs tracking operations solely by driving the carriage 3 by means of the voice coil motor 6.
Therefore, a method has been recently proposed in which a fine motion actuator is mounted on a load beam, and tracking operation is performed only by moving the distal end of the load beam.
FIG. 11 is a perspective view of a conventional load beam on which piezoelectric elements acting as fine motion actuators are mounted. This load beam 11 consists of a stainless steel leaf spring, and has a fixed base end 11a held by the carriage and a swingable portion 11b swingable relative to the fixed base end 11a. On both sides of the front end of the fixed base end 11a, arms 11c and 11c extend in the lengthwise direction of the fixed base end 11a. The swingable portion 11b is connected to the arms 11c and 11c through elastic support members 11d and 11d. 
In addition, the swingable portion 11b and the fixed base end 11a carry piezoelectric elements 12 and 13 that bridge over a gap 11e. The piezoelectric elements 12 and 13 have piezoelectric layers 12b and 13b that are overlain and underlain by electrode layers 12a1 and 13a1, and by 12a2 and 13a2, respectively.
The load beam 11 shown in FIG. 11 is grounded. The electrode layers 12a1 and 13a1 of the piezoelectric elements 12 and 13 are grounded by being electrically connected to the load beam. The piezoelectric layers 12b and 13b of the piezoelectric elements 12 and 13, respectively, are polarized in the thicknesswise counter directions. Therefore, when the same potential is applied to the electrode layers 12a2 and 13a2, one of the piezoelectric elements expands while the other piezoelectric element contracts in the longitudinal direction.
As a result, the elastic support members 11d and 11d are distorted, causing a change in the posture of the slider 21 fixed on the distal end of the swingable portion 11b. In other words, it becomes possible to perform a tracking operation by moving the slider attached to the distal end of the swingable portion 11b in the widthwise direction of tracks. When the servo system is constituted by a load beam carrying piezoelectric elements mounted thereon, the servo band can be widened to 2 kHz or greater.
The piezoelectric elements 12 and 13 are elements that cause distortions when an electric voltage is applied to the electrode layers 12a1, 12a2, 13a1 and 13a2. On the other hand, the application of a stress on the piezoelectric elements 12 and 13 causes distortions in the piezoelectric elements 12 and 13, and generates a voltage between the electrode layers 12a1 and 12a2, as well as between 13a1 and 13a2.
In particular during the process of supersonic cleaning or transportation of the magnetic head apparatus, the piezoelectric elements 12 and 13 may be subjected to vibrations of a considerable magnitude that cause a very high voltage to be developed in the piezoelectric elements 12 and 13. When they come into contact with a conductor, a surge current may flow. This current can have a frequency of several hundreds to several thousands of MHz and a magnitude of several amperes. Such a high frequency current may generate an induced current in the neighboring conductive pattern. This high-frequency voltage leads to capacity couplings with the neighboring conductive patterns and the transportation of electric currents. For example, during cleaning, the transportation of current occurs due to capacity coupling through the intermediary of water whose induction ratio is several dozen times greater than that of air. In particular, reproducing elements whose resistance against electric current is low were often destroyed by this electric current generated during supersonic cleaning and transportation.